The present invention is directed to bicycle derailleurs and, more particularly, to a motion resisting apparatus for a bicycle derailleur.
A typical bicycle derailleur comprises a base member for coupling to a bicycle frame, a movable member coupled for movement relative to the base member, and a chain guide coupled to the movable member for guiding a chain among a plurality of sprockets. In a rear derailleur, the chain guide supports an upper guide pulley and a lower tension pulley, and the chain guide is pivotably mounted to the movable member through a pivot shaft. A spring is mounted between the movable member and the chain guide for biasing the chain guide in a clockwise.
When the rear derailleur is mounted to the bicycle, the guide pulley is located below a plurality of rear sprockets that are mounted to the rear wheel. The bicycle chain coupled to the front sprocket assembly engages the top and rear of one of the plurality of rear sprockets, engages the front of the guide pulley, engages the rear of the tension pulley, and then returns to the front sprocket assembly. During riding, the chain moves from the currently engaged front sprocket, to the tension pulley, to the guide pulley, and then to the selected rear sprocket. Because the chain length is set so that the chain can engage the largest front sprocket and the largest rear sprocket, the chain experiences slack whenever the chain engages a smaller front sprocket and/or a smaller rear sprocket. When that occurs, the spring bias rotates the chain guide so that the tension pulley takes up the slack on the chain and prevents the chain from falling off of the sprockets.
Mountain bicycles, for example, typically are ridden over rough terrain at high speed. As a result, the bicycle often experiences severe vibrations. Such vibrations can cause the chain guide to rotate counterclockwise, thereby restoring the slack in the chain and causing the chain to malfunction. To prevent such malfunctions, some rear derailleurs include one-way or bidirectional dampers that resist sudden movement of the chain guide, and some rear derailleurs include hydraulic shock absorbers that resist sudden movement of the chain guide.